Dynamic bone fixation element and method of using the same

ABSTRACT

The present invention relates to dynamic bone fixation elements and a surgical method to stabilize bone or bone fragments. The dynamic bone fixation elements preferably include a bone engaging component and a load carrier engaging component. The bone engaging component preferably includes a plurality of threads for engaging a patient&#39;s bone and a lumen. The load carrier engaging component preferably includes a head portion for engaging a load carrier (e.g., bone plate) and a shaft portion. The shaft portion preferably at least partially extends into the lumen. Preferably at least a portion of an outer surface of the shaft portion is spaced away from at least a portion of an inner surface of the lumen via a gap so that the head portion can move with respect to the bone engaging component. The distal end of the shaft portion is preferably coupled to the lumen.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/332,756 filed Dec. 11, 2008, which claims priority to U.S.Provisional Patent Application Ser. No. 61/014,308, filed Dec. 17, 2007,entitled “Dynamic Fixation System”; U.S. Provisional Patent ApplicationSer. No. 61/041,824, filed Apr. 2, 2008, entitled “Dynamic FixationSystem”; and U.S. Provisional Patent Application Ser. No. 61/075,396,filed Jun. 25, 2008, entitled “Stress Controlled Bone Fixation”; thecontents of each of which are hereby incorporated by reference in theirentirety.

BACKGROUND

Millions of people suffer from bone fractures each year. Treatment ofthis condition is frequently accomplished by rigid fixation whichinvolves the use of implants such as, for example, longitudinal loadcarriers (e.g., bone plates, rods, etc.) fixed to a patient's bone orbone fragments via a plurality of bone fixation elements (e.g., bonescrews, hooks, pins, rivets, etc.) in order to stabilize the fracturedbone across the fracture.

The use of flexible or dynamic fixation in bone fixation is believed toprovide advantages by reducing the amount of stress generally associatedwith rigid fixation, and thus better protect the patient's bone or bonefragments.

SUMMARY

The present invention relates generally to surgical devices and methodsto stabilize bones or bone fragments. More specifically, the presentinvention relates to a dynamic bone fixation element, and a surgicalmethod/procedure to stabilize a bone or bone fragments using the same.

In one exemplary embodiment of the present invention, the dynamic bonefixation element preferably includes a bone engaging component and aload carrier engaging component. The bone engaging component preferablyincludes a proximal end, a distal end, and a lumen extending at leastpartially from the proximal end of the bone engaging component. Thelumen defines an inner surface. The load carrier engaging componentpreferably includes a head portion for engaging a load carrier and ashaft portion extending from the head portion. The shaft portionpreferably includes a proximal end, a distal end and an outer surface.The shaft portion is preferably sized and configured to at leastpartially extend into the lumen formed in the bone engaging component.Preferably at least a portion of the shaft portion has a diameter D_(S)and at least a portion of the lumen has a diameter D_(L), the diameterD_(L) being greater than the diameter D_(S) so that at least a portionof the outer surface of the shaft portion is spaced away from at least aportion of the inner surface of the lumen. In addition, preferably, thedistal end of the shaft portion is coupled to the lumen at a positiondistally of the proximal end of the bone engaging component so that thehead portion moves with respect to the bone engaging component and hencethe engaged bone or bone fragments may move with respect to the loadcarrier to enable micro-movement. The inner surface of the lumen may betapered at an angle θ such that the diameter D_(L) of the lumen at aproximal end thereof is larger than the diameter D_(L) of the lumen at aposition distally of the proximal end. The taper angle θ of the lumen ispreferably between about zero degrees to about ten degrees. The shaftportion is preferably integrally formed with the head portion. The shaftportion is preferably coupled to the bone engaging component within thelumen at a position proximate to the distal end of the bone engagingcomponent. The shaft portion is preferably coupled to the bone engagingcomponent within the lumen via a press fit connection. The distal end ofthe shaft portion preferably has a diameter greater than the diameterD_(L) of the lumen. Alternatively and/or in addition, the shaft portionmay include one or more textured surfaces formed thereon. The texturedsurfaces are preferably elastically deformable so that the texturedsurfaces deform as the shaft portion is being inserted into the lumen.Thereafter the textured surfaces preferably return to their largeroriginal size so that the textured surface press against the innersurface of the lumen to increase a contact pressure between the outersurface of the shaft portion and the inner surface of the lumen. Thetextured surface may be in the form of a plurality of radially extendingridges formed on a portion of the shaft portion. Alternatively and/or inaddition, the textured surface may be in the form of a plurality oflongitudinal extending ridges formed on a portion of the shaft portion.

Alternatively and/or in addition, the outer surface of the bone engagingcomponent preferably includes a plurality of threads formed on the outersurface thereof for engaging the patient's bone or bone fragments, theouter surface of the shaft portion may be welded to the inner surface ofthe lumen by welding in-between adjacent threads formed on the outersurface of the bone engaging component.

The head portion preferably includes a driving element for engaging atip formed on a drive tool. For example, the head portion may include aplurality of through holes for receiving a plurality of pins formed onthe tip of the drive tool, the pins being sized and configured to extendthrough the head portion of the load carrier engaging component and intocontact with the bone engaging component so that the plurality of pinscontact both the load carrier engaging component and the bone engagingcomponent such that rotation of the drive tool simultaneously rotatesboth the load carrier engaging component and the bone engagingcomponent. Alternatively, for example, the head portion may include oneor more projections extending therefrom and the bone engaging componentincludes one or more recesses formed therein so that the projectionextends into the recess so that rotation of the drive toolsimultaneously rotates both the load carrier engaging component and thebone engaging component.

In another exemplary embodiment, the present invention is directed to amethod for internally fixing a load carrier across a fracture in a bone.The method includes the steps of (a) providing a plurality of dynamicbone fixation elements; (b) making an incision; and (c) coupling theload carrier to the patient's bone via two or more dynamic bone fixationelements on either side of the fracture so that the dynamic bonefixation elements enable parallel movement of the bone or bone fragmentsacross the fracture; and (d) closing the incision so that the loadcarrier and plurality of dynamic bone fixation elements remain withinthe patient. Preferably the dynamic bone fixation elements each includea bone engaging component for engaging the bone and a load carrierengaging component for engaging the load carrier, the bone engagingcomponent being moveably associated with the load carrier engagingcomponent so that movement of the load carrier engaging component withrespect to the bone engaging component enables the parallel movement ofthe bone or bone fragments across the fracture. The bone engagingcomponent preferably includes a lumen extending at least partially froma proximal end of the bone engaging component, the lumen defining aninner surface. The load carrier engaging component preferably includes ahead portion for engaging the load carrier and a shaft portion extendingfrom the head portion, the shaft portion having a proximal end, a distalend and an outer surface, the shaft portion being sized and configuredto at least partially extend into the lumen formed in the bone engagingcomponent. Preferably, at least a portion of the outer surface of theshaft portion is spaced away from at least a portion of the innersurface of the lumen so that the head portion moves with respect to thebone engaging component.

The method for fixing the load carrier across the fracture in the bonemay also include inserting one or more standard bone screws on one orboth sides of the fracture F so that micro-movement of the bone isprevented for an initial period of time so that thereafter the standardbone screws may be removed from the patient's bone after the initialperiod of time has lapsed so that micro-movement of the bone is enabled.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe preferred embodiments of the application, will be better understoodwhen read in conjunction with the appended drawings. For the purposes ofillustrating the preferred dynamic bone fixation elements and surgicalprocedure and/or method of the present application, there is shown inthe drawings preferred embodiments. It should be understood, however,that the application is not limited to the precise arrangements andinstrumentalities shown. In the drawings:

FIG. 1 shows a cross-sectional view of a dynamic bone fixation elementaccording to a first exemplary embodiment of the present invention;

FIG. 2 shows a cross-sectional view of a dynamic bone fixation elementaccording to a second exemplary embodiment of the present invention;

FIG. 3 shows a cross-sectional view of a dynamic bone fixation elementaccording to a third exemplary embodiment of the present invention;

FIG. 3A shows a cross-sectional view of an alternate embodiment of thedynamic bone fixation element shown in FIG. 3, the cross-sectional viewillustrating preferred, exemplary dimensions of the dynamic bonefixation element;

FIG. 3B shows a cross-sectional view of an alternate embodiment of thedynamic bone fixation element shown in FIG. 3, the cross-sectional viewillustrating an exemplary dynamic bone fixation element for use inspinal procedures;

FIG. 3C shows a cross-sectional view of an alternate embodiment of thedynamic bone fixation element shown in FIG. 3, the cross-sectional viewillustrating an exemplary dynamic bone fixation element for use intrauma procedures;

FIG. 4A shows a detailed view of a plurality of radially extendingridges or lamellas formed on a distal end of a shaft portion of a loadcarrier engaging component in accordance with one exemplary embodimentof the load carrier engaging component;

FIG. 4B shows a detailed view of a plurality of longitudinally extendingridges or lamellas formed on a distal end of a shaft portion of a loadcarrier engaging component in accordance with one exemplary embodimentof the load carrier engaging component;

FIG. 4C shows a detailed view of a plurality of radially extendingridges or lamellas and a plurality of longitudinally extending ridges orlamellas formed on a distal end of a shaft portion of a load carrierengaging component in accordance with one exemplary embodiment of theload carrier engaging component;

FIG. 5A shows a side view of an exemplary method for coupling a shaftportion of a load carrier engaging component to a bone engagingcomponent in accordance with one exemplary embodiment of the presentinvention;

FIG. 5B shows a cross sectional view of the exemplary method forcoupling the shaft portion of the load carrier engaging component to thebone engaging component taken along line 5B-5B shown in FIG. 5A;

FIG. 6A shows an exploded, perspective view of a drive element forcoupling a head portion of a dynamic bone fixation element to a drivetool in accordance with a first preferred embodiment of the presentinvention;

FIG. 6B shows a side view of the drive element coupled to the headportion of the drive tool shown in FIG. 6A;

FIG. 6C shows a side view of a drive element for coupling a head portionof a dynamic bone fixation element to a drive tool in accordance with asecond preferred embodiment of the present invention;

FIG. 7 shows a cross section view of the dynamic bone fixation elementsinterconnecting a load carrier to a patient's bone;

FIG. 8 shows a cross-sectional view of an exemplary method for long bonefixation in accordance with a first exemplary surgical method of thepresent invention;

FIG. 9 shows a second cross-sectional view of the exemplary method forlong bone fixation shown in FIG. 8;

FIG. 10 shows a cross-sectional view of an exemplary method for longbone fixation in accordance with a second exemplary surgical method ofthe present invention;

FIG. 11A shows a cross-sectional view of an exemplary method for longbone fixation in accordance with a third exemplary surgical method ofthe present invention;

FIG. 11B shows a second cross-sectional view of the exemplary method forlong bone fixation shown in FIG. 11A;

FIG. 12 shows a cross-sectional view of a dynamic bone fixation elementaccording to a fourth exemplary embodiment of the present invention;

FIG. 13 shows a cross-sectional view of a dynamic bone fixation elementaccording to a fifth exemplary embodiment of the present invention;

FIG. 14 shows a cross-sectional view of a dynamic bone fixation elementaccording to a sixth exemplary embodiment of the present invention;

FIG. 15 shows a cross-sectional view of a dynamic bone fixation elementaccording to a seventh exemplary embodiment of the present invention;

FIG. 16A shows a first detailed, cross-sectional view of a head portionof a dynamic bone fixation element according to an eighth exemplaryembodiment of the present invention;

FIG. 16B shows a second detailed, cross-sectional view of a head portionof a dynamic bone fixation element according to the eighth exemplaryembodiment of the present invention;

FIG. 16C shows a third detailed, cross-sectional view of a head portionof a dynamic bone fixation element according to the eighth exemplaryembodiment of the present invention;

FIG. 17 shows a partial cross-sectional view of a dynamic bone fixationelement according to a ninth exemplary embodiment of the presentinvention;

FIG. 18A shows a cross-sectional view of a dynamic pedicle screwfixation clamp according to a first exemplary embodiment of the presentinvention;

FIG. 18B shows a detailed, cross-sectional view of a portion of thedynamic pedicle screw fixation clamp shown in FIG. 18A;

FIG. 18C shows a cross-sectional view of an alternate embodiment of thedynamic pedicle screw fixation clamp shown in FIG. 18A;

FIG. 19 shows a cross-sectional view of a dynamic pedicle screw fixationclamp according to a second exemplary embodiment of the presentinvention;

FIG. 20A shows a cross-sectional view of a dynamic pedicle screwfixation clamp according to a third exemplary embodiment of the presentinvention;

FIG. 20B shows a cross-sectional view of the frame used in connectionwith the dynamic pedicle screw fixation clamp shown in FIG. 20A takenalong line 20B-20B of FIG. 20A;

FIG. 21A shows a cross-sectional view of a dynamic pedicle screwfixation clamp according to a fourth exemplary embodiment of the presentinvention;

FIG. 21B shows a detailed, cross-sectional view of the dynamic sectionof the connecting member used in connection with the dynamic pediclescrew fixation clamp shown in FIG. 21A;

FIG. 22 shows a cross-sectional view of a dynamic pedicle screw fixationclamp according to a fifth exemplary embodiment of the presentinvention;

FIG. 23 shows a cross-sectional view of an alternate embodiment of thedynamic pedicle screw fixation clamp shown in FIG. 22; and

FIG. 24 shows a cross-sectional view of a dynamic pedicle screw fixationclamp according to a sixth exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION

Certain terminology is used in the following description for convenienceonly and is not limiting. The words “right”, “left”, “top” and “bottom”designate directions in the drawings to which reference is made. Thewords “inwardly” and “outwardly” refer to directions toward and awayfrom, respectively, the geometric center of the device and designatedparts thereof. The words, “anterior”, “posterior”, “superior”,“inferior” and related words and/or phrases designate preferredpositions and orientations in the human body to which reference is madeand are not meant to be limiting. The terminology includes theabove-listed words, derivatives thereof and words of similar import.

Certain exemplary embodiments of the invention will now be describedwith reference to the drawings. In general, the present inventionrelates to a dynamic bone fixation element 10, 10′, 10″, and a surgicalprocedure and/or method for the flexible or dynamic fixation of apatient's bone or bone fragments B. More specifically, the presentinvention relates to various embodiments of a dynamic bone fixationelement 10, 10′, 10″, and a surgical procedure and/or method forinternal long bone fixation using a plurality of dynamic bone fixationelements 10, 10′, 10″ to stabilize a patient's bone B across a fracturesite F. As generally understood by one of ordinary skill in the art, itshould be understood that while the dynamic bone fixation elements 10,10′, 10″, and surgical procedure and/or method for internal long bonefixation will be described in connection with a patient's long bone Bsuch as, for example, a femur (thigh), tibia and fibula (leg), humerus(upper arm), radius and ulna (lower arm), etc., those skilled in the artwill appreciate that the dynamic bone fixation elements 10, 10′, 10″,and surgical procedure and/or method for long bone fixation may be usedin other surgical procedures such as, for example, in spinal surgeries,maxillofacial bone fixation, external fixation, etc.

Generally speaking, as will be described in greater detail below, adynamic bone fixation element 10, 10′, 10″ preferably includes a firstbone engaging component 20, 20′, 20″ such as, for example, an externallythreaded bone screw, a hook, a bolt, a pin, a rivet, etc., and a secondlongitudinal load carrier engaging component 40, 40′, 40″ such as, forexample, an enlarged head portion 42, 42′, 42″. The load carrierengaging component 40, 40′, 40″ is movably associated with the boneengaging component 20, 20′, 20″ so that in use incorporation of thedynamic bone fixation element 10, 10′, 10″ enables movement of the loadcarrier engaging component 40, 40′, 40″ with respect to the boneengaging component 20, 20′, 20″ so that the engaged bone B may move withrespect to the load carrier 12. That is, as will be described in greaterdetail below, the load carrier engaging component 40, 40′, 40″ includesa head portion 42, 42′, 42″ for engaging, for example, a bone plate 12or rod, and a shaft portion 50, 50, 50″. The bone engaging component 20,20′, 20″ includes, for example, a plurality of external threads 27, 27′,27″ for engaging a patient's bone B and an inner lumen 28, 28′, 28″ forreceiving at least a portion of the shaft portion 50, 50′, 50″. Theouter surface 56, 56′, 56″ of the shaft portion 50, 50′, 50″ and theinner surface 30, 30′, 30″ of the lumen 28, 28′, 28″ are preferablysized and configured such that there is a clearance or gap therebetween.In addition, the head portion 42, 42′, 42″ of the load carrier engagingcomponent 40, 40′, 40″ is not directly coupled to the bone engagingcomponent 20, 20′, 20″ so that, preferably, there is a clearance or gapbetween the distal end 46, 46′, 46″ of the head portion 42, 42′, 42″ andthe proximal end 22, 22′, 22″ of the bone engaging component 20, 20′,20″. Therein, insertion of the shaft portion 50, 50′, 50″ of the loadcarrier engaging component 40, 40′, 40″ into the lumen 28, 28′, 28″formed in the bone engaging component 20, 20′, 20″ enables the dynamicbone fixation element 10, 10′, 10″ to flex and/or move in order toenable and/or absorb micro-movement of the bone B with respect to theload carrier 12.

Referring to FIG. 1, the dynamic bone fixation element 10 of a firstpreferred embodiment preferably includes a first bone engaging component20 such as, for example, an externally threaded bone screw for engaginga patient's bone B, and a second load carrier engaging component 40 suchas, for example, an enlarged head portion 42. The externally threadedbone screw includes an inner lumen 28 for receiving a shaft portion 50extending from the head portion 42 of the load carrier engagingcomponent 40. That is, the bone engaging component 20 includes aproximal end 22, a distal end 24, an outer surface 26 and a lumen 28.The lumen 28 extends at least partially through the bone engagingcomponent 20 from the proximal end 22 to an end 25 proximal of thedistal end 24.

In a preferred embodiment, the outer surface 26 of the bone engagingcomponent 20 includes a plurality of threads 27 extending along a lengththereof for engaging the fractured bone or bone fragments B. The angleand the shape of the threads 27 may be varied to meet specific anchoringneeds, such as, for example, in osteoporotic bones. The distal end 24 ofthe bone engaging component 20 may be tapered to include a self-tappingor a self-drilling tip as would be understood by those skilled in theart.

The load carrier engaging component 40 includes a shaft portion 50having an outer surface 56, and the head portion 42. The shaft portion50 extends longitudinally from a proximal end 52 to a distal end 54 andis sized and shaped to at least partially fit within the lumen 28 of thebone engaging component 20. As shown, the head portion 42 may protruderadially outward from the proximal end 52 of the shaft portion 50 with aradius greater than that of the outer surface 56 of the shaft portion50. The entire shaft portion 50 may be received within the lumen 28 suchthat the distal end 46 of the head portion 42 abuts the proximal end 22of the bone engaging component 20.

Alternatively, referring to a second embodiment of the dynamic bonefixation element 10′ as best shown in FIG. 2, the lumen 28′ formed inthe bone engaging component 20′ may be shorter than a length of theshaft portion 50′ extending from the head portion 42′ of the loadcarrier engaging portion 40′ such that only a portion of the shaftportion 50′ fits within the lumen 28′ while a neck portion 31′ protrudesfrom the bone engaging component 20′. The neck portion 31′ may flexpermitting the head portion 42′ to move relative to the distal portion54′ of the shaft portion 50′ and/or relative to the bone engagingcomponent 20′. In use, the neck portion 31′ of the dynamic bone fixationelement 10′ is preferably positioned between a bone facing surface 13 ofthe load carrier 12 and the patient's bone or bone fragments B such thatthe neck portion 31′ may move and/or deform as necessary to accommodatemicro-movement of the patient's bone or bone fragments B.

Preferably, referring to a third preferred embodiment of the dynamicbone fixation element 10″ as best shown in FIGS. 3-3C, the shaft portion50″ extending from the head portion 42″ of the load carrier engagingcomponent 40″ has a diameter D_(S) smaller than a diameter of the lumenD_(L) formed in the bone engaging component 20″ such that a gap (e.g.,an annular space) exists between the outer surface 56″ of the shaftportion 50″ and an inner surface 30″ of the lumen 28″ so that the headportion 42″ can move relative to the bone engaging component 20″.Preferably the dynamic bone fixation element 10″ allows about twomillimeters of movement of the head portion 42″ away from a longitudinalaxis 11″ of the dynamic bone fixation element 10″. In other embodimentsmore or less flexing of the shaft portion 50″ and more or less movementof the head portion 42″ is possible. The distal end 54″ of the shaftportion 50″ is preferably coupled and/or attached to the lumen 28″ atend 25″ such that the shaft portion 50″ has greater freedom of movementwithin the lumen 28″, as will be described in greater detail below. Itwill be understood by those of skill in the art that the size of the gapmay be adjusted to adjust the amount of permitted movement between thebone engaging component 20″ and the load carrier engaging component 40″.

In addition and/or alternatively, the lumen 28″ formed in the boneengaging component 20″ may be tapered such that a diameter of the lumen28″ at the proximal end 22″ of the bone engaging component 20″ is largerthan a diameter of the lumen 28″ at end 25″. The taper angle θ of thelumen 28″ may be between about zero to about ten degrees. It will beunderstood by those of skill in the art that the taper angle θ may beadjusted to adjust the amount of permitted movement between the boneengaging component 20″ and the load carrier engaging component 40″. Inuse, the size of the taper angle θ may be used to limit the maximumamount of movement between the head portion 42″ of the load carrierengaging component 40″ and the bone engaging component 20″ by limitinghow far the shaft portion 50″ may flex and/or move before the outersurface 56″ of the shaft portion 50″ contacts the inner surface 30″ ofthe lumen 28″ formed in the bone engaging component 20″. It should benoted that the outer surface 56″ of the shaft portion 50″ may be taperedinstead of or in addition to tapering the inner surface 30″ of the lumen28″. Alternatively and/or in addition, the distal end 46″ of the headportion 42″ and the proximal end 22″ of the bone engaging component 20″may be angled (angle α) to provide increased clearance between the headportion 42″ and the bone engaging component 20″.

With particular reference to FIGS. 3B and 3C, to satisfy the differentloads anticipated in spine and trauma procedures, generally speaking,for spinal applications (as best shown in FIG. 3B), preferably thedistal end 54″ of the shaft 50″ has a larger diameter than the proximalend 52″ of the shaft 50″ to accommodate the higher anticipated stressesthat the distal end 54″ of the shaft 50″ is expected to experience.Thus, for spine specific embodiments where straight bending as opposedto S-bending is expected, the outer surface 56″ of the shaft 50″ ispreferably tapered so that the distal end 54″ of the shaft 50″ has alarger diameter than the proximal end 52″ of the shaft 50″. In addition,the lumen 28″ formed in the bone engaging component 20″ preferablyincludes one or more conically or “stepped” cylindrically shapedsurfaces 29″ to accommodate the increased motion of the shaft 50″ withrespect to the bone engaging component 20″. As shown, the lumen 28″ mayalso include a “trumpet”-shaped distal end and the shaft 50″ may includea conical shape with an ellipsoid neck at the head portion and a lip 53″at the proximal end thereof for contacting the proximal end 22″ of thebone engaging component 20″.

This is in contrast to trauma applications (as best shown in FIG. 3C)such as, long bone fixation, where it is generally not necessary toincrease the diameter of the distal end 54″ of the shaft 50″ since theshaft 50″ generally undergoes S-bending (something it won't do in spineapplications) and hence, in trauma applications, the distal and proximalends 52″, 54″ of the shaft 50″ experience approximately the same amountof force. Thus, preferably trauma-specific embodiments can include ashaft 50″ that has a constant diameter for the entire length or most ofthe length of the shaft 50″, which is easier to manufacture than a shaft50″ that gradually increases in diameter or has an increased diameterportion at the distal end 54″ thereof. As shown, for trauma specificembodiments where S-bending is expected, the lumen 28″ may include acylindrical shape and a trumpet-shaped distal end while the shaft 50″may include a cylindrical shape and an ellipsoid-shaped neck at the headportion.

The shaft portion 50, 50′, 50″ may be integrally formed with the headportion 42, 42′, 42″. Alternatively, the shaft portion 50, 50′, 50″ maybe coupled to the head portion 42, 42′, 42″ by any means now orhereafter known including but not limited to adhesive, welding,soldering, brazing, press-fit, friction fit, interference fit, athreaded connection, pinning, shrinking, engrailing, a cotter-pin, oneor more fasteners such as via a pin or screw inserted longitudinally orradially, etc. In addition, the shaft portion 50, 50′, 50″ may be anysize, shape and configuration including but not limited to straight,tapered, curved, solid, hollow, slotted, or formed as a spring likemember such as, for example, a helical spring.

The head portion 42, 42′, 42″ may also include a plurality of externalthreads 43, 43′, 43″ for engaging the load carrier 12 such that thedynamic bone fixation element 10, 10′, 10″ may be locked to the loadcarrier 12. It will be understood by those of skill in the art that theload carrier 12 includes a plurality of openings 14 through which thedynamic bone fixation elements 10, 10′, 10″ are inserted into the boneor bone fragments B and that the openings 14 may be threaded to engagethe threading 43, 43′, 43″ formed on the head portion 42, 42′, 42″ ofthe load carrier engaging component 40, 40′, 40″. The head portion 42,42′, 42″ preferably also includes a driving element 60, as will bedescribed in greater detail below. It will also be understood by thoseof skill in the art that the head portion 42, 42′, 42″ may take any sizeand shape so long as the head portion 42, 42′, 42″ is structured toengage the load carrier 12 in a desired manner.

The shaft portion 50, 50′, 50″ of the load carrier engaging component40, 40′, 40″ may be integrally formed with the bone engaging component20, 20′, 20″. Alternatively, the shaft portion 50, 50′, 50″ of the loadcarrier engaging component 40, 40′, 40″ may be coupled to the boneengaging component 20, 20′, 20″, preferably within the lumen 28, 28′,28″, by any means now or hereafter known including but not limited toadhesive, welding, soldering, brazing, press-fit, friction fit,interference fit, a threaded connection, pinning, shrinking, engrailing,a cotter-pin, one or more fasteners such as via a pin or screw insertedlongitudinally or radially, etc.

Preferably, the shaft portion 50, 50′, 50″ of the load carrier engagingcomponent 40, 40′, 40″ is coupled to the bone engaging component 20,20′, 20″ within the lumen 28, 28′, 28″ formed in the bone engagingcomponent 20, 20′, 20″. That is, in a preferred embodiment, the shaftportion 50, 50′, 50″ is inserted into the lumen 28, 28′, 28″ andattached to the bone engaging component 20, 20′, 20″ at end 25, 25′,25″, located distally of the proximal end 22, 22′, 22″ of the boneengaging component 20, 20′, 20″, and more preferably adjacent orproximate to the distal end 24, 24′, 24″ of the bone engaging component20, 20′, 20″. More preferably, the shaft portion 50, 50′, 50″ of theload carrier engaging component 40, 40′, 40″ is secured within the lumen28, 28′, 28″ formed in the bone engaging component 20, 20′, 20″ by apress fit. That is, generally speaking, the diameter D_(L) of the lumen28, 28′, 28″ formed in the bone engaging component 20, 20′, 20″ isslightly smaller than the diameter D_(S) of at least a portion of theshaft portion 50, 50′, 50″ (preferably the distal end 54, 54′, 54″ ofthe shaft portion 50, 50′, 50″) so that some amount of force is requiredto insert and remove the shaft portion 50, 50′, 50″ from the boneengaging component 20, 20′, 20″. In this manner, the press fitengagement of the shaft portion 50, 50′, 50″ with the bone engagingcomponent 20, 20′, 20″ ensures that the load carrier engaging component40, 40′, 40″ will not separate from the bone engaging component 20, 20′,20″ and enables transfer of longitudinal and torsional forces betweenthe load carrier engaging component 40, 40′, 40″ and the bone engagingcomponent 20, 20′, 20″.

Referring to FIGS. 4A-4C, in order to increase the coupled strengthbetween the load carrier engaging component 40, 40′, 40″ and the boneengaging component 20, 20′, 20″, the shaft portion 50, 50′, 50″ of theload carrier engaging component 40, 40′, 40″ may include one or moretextured surfaces 80 formed thereon. In use, the textured surfaces 80are sized and configured, either in connection with the diameter D_(S)of the shaft portion 50, 50′, 50″ or alone, to be slightly oversized ascompared to the diameter D_(L) of the lumen 28, 28′, 28″ formed in thebone engaging component 20, 20′, 20″. During assembly, the texturedsurfaces 80 deform as the shaft portion 50, 50′, 50″ is being insertedinto the lumen 28, 28′, 28″ formed in the bone engaging component 20,20′, 20″. Thereafter, preferably due to material elasticity, thetextured surface 80 returns to its original size thereby causing thetextured surface 80 to press against the inner surface 30, 30′, 30″ ofthe lumen 28, 28′, 28″ to increase the resistance against the shaftportion 50, 50′, 50″ moving and/or separating from the bone engagingcomponent 20, 20′, 20″. That is, providing textured surfaces 80 on theouter surface 56, 56′, 56″ of the shaft portion 50, 50′, 50″ increasesthe contact pressure between the outer surface 56, 56′, 56″ of the shaftportion 50, 50′, 50″ and the inner surface 30, 30′, 30″ of the lumen 28,28′, 28″ and thus increases the transferable forces and the contactstrength between the shaft portion 50, 50′, 50″ and the bone engagingcomponent 20, 20′, 20″. As best shown in FIG. 4A, the textured surface80 may be in the form of a plurality of radially extending ridges orlamellas 82 formed on a portion of the shaft portion 50, 50′, 50″,preferably adjacent to the distal end 54, 54′, 54″ of the shaft portion50, 50′, 50″. Providing radial ridges or lamellas 82 increases the axialor pull out strength of the shaft portion 50, 50′, 50″ with respect tothe bone engaging component 20, 20′, 20″. Alternatively, as best shownin FIG. 4B, the textured surface 80 may be in the form of a plurality oflongitudinal extending ridges or lamellas 84 formed on a portion of theshaft portion 50, 50′, 50″, preferably adjacent to the distal end 54,54′, 54″ of the shaft portion 50, 50′, 50″. Providing longitudinalridges or lamellas 84 increases the torque or torsional strength of theshaft portion 50, 50′, 50″ with respect to the bone engaging component20, 20′, 20″. Alternatively, as best shown in FIG. 4C, the shaft portion50, 50′, 50″ may include a plurality of radial ridges or lamellas 82 anda plurality of longitudinal ridges or lamellas 84 in order to increaseboth the axial and torsional strength of the shaft portion 50, 50′, 50″with respect to the bone engaging component 20, 20′, 20″. As will beappreciated by one of ordinary skill in the art the ridges or lamellas82, 84 may have other shapes including, for example, spiral shaped.

Alternatively and/or in addition, as best shown in FIGS. 5A and 5B, theshaft portion 50, 50′, 50″ may be inserted into the lumen 28, 28′, 28″formed in the bone contacting component 20, 20′, 20″ and welded W to thebone contacting component 20, 20′, 20″. The shaft portion 50, 50′, 50″may be welded W to the bone contacting component 20, 20′, 20″ from theoutside of the dynamic bone fixation element 10, 10′, 10″ by spiralingwelding W between adjacent threads 27, 27′, 27″ formed on the outersurface 26, 26′, 26″ of the bone contacting component 20, 20′, 20″. Byusing the threads 27, 27′, 27″ as a weld path, damage to the threadprofile of the bone engaging component 20, 20′, 20″ is minimized. Theshaft portion 50, 50′, 50″ may be welded W to the bone contactingcomponent 20, 20′, 20″ by any appropriate welding process now orhereafter known including but not limited to laser welding, electronbeam welding, resistance stud welding, etc. As will be appreciated byone of ordinary skill in the art, the shaft portion 50, 50′, 50″ of theload carrier engaging component 40, 40′, 40″ may be welded W to the boneengaging component 20, 20′, 20″ with or without the incorporation of apress-fit or some other means for coupling. Moreover, the press-fit maybe incorporated with or without the textured surfaces 80 (e.g., theradial and/or longitudinal ridges or lamellas 82, 84).

As previously mentioned, the head portion 42, 42′, 42″ preferably alsoincludes a driving element 60 for engaging a corresponding tip 62 formedon a drive tool 64, such as a screw driver for rotating the dynamic bonefixation element 10, 10′, 10″ into engagement with the patient's bone orbone fragments B. The driving element 60 may have any form now orhereafter known including, but not limited to, an external hexagon, astar drive pattern, a Phillips head pattern, a slot for a screw driver,a threading for a correspondingly threaded post, an internal recess,etc. It will also be understood by those of skill in the art that thedriving element 60 may be of any shape or structure so long as itpermits the driving element 60 to drive the dynamic bone fixationelement 10, 10′, 10″ into a desired location in the patient's bone orbone fragments B.

Preferably, in order to engage the head portion 42, 42′, 42″ of the loadcarrier engaging component 40, 40′, 40″ and to rotate the bone engagingcomponent 20, 20′, 20″ without slipping or separating the load carrierengaging component 40, 40′, 40″ from the bone engaging component 20,20′, 20″, the head portion 42, 42′, 42″ of the load carrier engagingcomponent 40, 40′, 40″ includes a plurality of through holes 68 forreceiving a plurality of pins 63 extending from a distal end of thedrive tool 64 as best shown in FIGS. 6A and 6B. The plurality of pins 63being sized and configured to extend through the head portion 42, 42′,42″ of the load carrier engaging component 40, 40′, 40″ and into contactwith the bone engaging component 20, 20′, 20″ so that the plurality ofpins 63 contact both the load carrier engaging component 40, 40′, 40″and the bone engaging component 20, 20′, 20″ such that rotation of thedrive tool 64 simultaneously rotates both the load carrier engagingcomponent 40, 40′, 40″ and the bone engaging component 20, 20′, 20″.

Alternatively, as best shown in FIG. 6C, the head portion 42, 42′, 42″of the load carrier engaging component 40, 40′, 40″ may include one ormore projections 70 extending therefrom and the bone engaging component20, 20′, 20″ may include one or more recesses 72 formed therein so thatthe projection 70 extends into the recess 72 so that rotation of thedrive tool 64 simultaneously rotates both the load carrier engagingcomponent 40, 40′, 40″ and the bone engaging component 20, 20′, 20″.Preferably, the recess 72 has a length larger than the length of theprojection 70 so that some initial rotation of the head portion 42, 42′,42″ is permitted prior to the projection 70 contacting the recess 72. Aswill be appreciated by one of ordinary skill in the art, the recess 72may be formed on the head portion 42, 42′, 42″ and the projection 70 maybe formed on the bone engaging component 20, 20′, 20″.

In use, as best shown in FIG. 7, the dynamic bone fixation element 10,10′, 10″ may fix bones or bone fragments B of a broken bone to oneanother by coupling a load carrier 12 such as a plate to a patient'sbone or bone fragments B via two or more dynamic bone fixation elements10, 10′, 10″. In an exemplary embodiment, the load carrier 12 may be aplate that is positioned along the bone B such that it extends across afracture F separating the bone fragments B from one another. Once theload carrier 12 has been appropriately positioned, a dynamic bonefixation element 10, 10′, 10″ may be inserted into a first opening 14formed in the plate 12 until the head portion 42, 42′, 42″ engages thefirst opening 14 and the bone engaging component 20, 20′, 20″ engagesthe first bone fragment B on one side of the bone fracture F. A seconddynamic bone fixation element 10, 10′, 10″ may be inserted into a secondopening 14 formed in the plate 12 in substantially the same manner asdescribed above such that the second dynamic bone fixation element 10,10′, 10″ engages the second bone fragment B. Thus, the dynamic bonefixation element 10, 10′, 10″ may be used to fix bone fragments B to oneanother. It will be understood by those of skill in the art that anynumber of dynamic bone fixation element 10, 10′, 10″ may be used toattach the load carrier 12 to the bone or bone fragments B.

Exemplary Surgical Procedure/Method

Generally speaking, the human bone B is formed by a hard, thinnercortical outer portion surrounding a softer cancellous inner portion sothat when view in cross-section, the human bone B includes a first layerof cortical bone, an intermediate layer of cancellous bone and a secondlayer of cortical bone. Rigid fixation generally includes the fixationof one or more bone screws on either side of a fracture F formed in thebone B. In use resulting stress on the fractured bone B causes bendingof the bone B and plate 12 which, in turn, results in compression of thesecond layer of cortical bone (e.g., layer of cortical bone farthestfrom the plate 12). With standard bone screws 5 there is substantiallyzero movement in the plate 12 since the plate 12 is too rigid it can notbe compressed in a way that permits movement within the first layer ofthe cortical bone (e.g., layer of cortical bone nearest the plate 12),as such, generally speaking, there is clinically no forming of callus inthe first layer of cortical bone. However, incorporation of dynamic bonefixation elements 10, 10′, 10″ enable the first layer of the corticalbone (e.g., layer of cortical bone nearest the plate 12) to move andhence facilitate the formation of callus in both the first and secondlayers of cortical bone. That is, incorporation of dynamic bone fixationelements 10, 10′, 10″ enable parallel movement of the bone fragments Bwith respect to one another which in turn results in micro-movement ofboth layers of the cortical bone and hence facilitates the formation ofcallus in both the first and second layers of cortical bone.

More specifically, referring to FIGS. 8 and 9, an exemplary procedurefor internal long bone fixation in accordance with one aspect of thepresent invention involves using two or more dynamic bone fixationelements 10, 10′, 10″ on either side of a fracture F so that theresulting movement of the head portion 42, 42′, 42″ of the load carrierengaging component 40, 40′, 40″ with respect to the bone engagingcomponent 20, 20′, 20″ enables, in addition to bending, parallelmovement of the bone or bone fragments B across the fracture F. Thus, byincorporating two or more dynamic bone fixation elements 10, 10′, 10″ onboth sides of the fracture F, the preferred exemplary surgical procedureenables better healing across the fracture F as the bone/bone fragmentsB on either side of the first layer of cortical bone (e.g., layer ofcortical bone nearest the plate 12) remain in constant contact which iscontrary to prior art rigid fixation systems wherein the bone B issubjected to bending stress only. That is, when used in connection withan internal trauma application, when two or more dynamic bone fixationelements 10, 10′, 10″ are attached to a single bone or bone fragment B,the shaft portion 50, 50′, 50″ is forced to adopt a generally “S” shapedconfiguration generally parallel to one another to accommodate themicro-movements of the attached bone or bone fragment B.

When contrasted with external dynamic fixation such as, for example, viaexternal Schanz screws, internal dynamic fixation is completely internalthereby reducing the risk of infection generally associated withexternal Schanz screws. In addition, with internal dynamic bonefixation, the bone-screw interface of the dynamic bone fixation elements10, 10′, 10″ remain motionless because all of the dynamic motion occurswithin the lumen 28, 28′, 28″. In contrast, with external dynamic bonefixation, the S-bending in the external Schanz screws occurs along thelength of the screw that forms the bone-screw interface so that bendingin the external Schanz screws gradually weakens the adherence of thescrew in the bone.

Incorporation of a single dynamic bone fixation element 10, 10′, 10″ oneither side of the fracture F is insufficient since using a singledynamic bone fixation element 10, 10′, 10″ on either side of thefracture F permits each of the bone fragments B to bend towards the loadcarrier 12 (e.g., angulation between the plate 12 and the bone B ispermitted). The bone fragments B are allowed to rotate around the screwaxis. In addition, using a single dynamic bone fixation element 10, 10′,10″ on either side of the fracture F permits the dynamic bone fixationelements 10, 10′, 10″ to bend. Thus, using a single dynamic bonefixation element 10, 10′, 10″ on either side of the fracture F decreasesthe overall stability of the construct during bone healing.

Alternatively, a second embodiment of an exemplary surgical procedure asbest shown in FIG. 10 may be carried out using two or more dynamic bonefixation elements 10, 10′, 10″ on one side of the fracture F whilestandard bone screws 5 may be used on the other side of the fracture F.Incorporation of standard bone screws 5 on one side of the fracture isparticularly beneficial wherein, for one reason or another, the surgeonneeds or desires to limit movement of the fractured bone to one side ofthe fracture only.

Alternatively and/or in addition, a third embodiment of an exemplarysurgical procedure as best shown in FIGS. 11A and 11B involves using oneor more standard bone screws 5 on one or both sides of the fracture F sothat micro-movement of the bone/bone fragments B is prevented for somelength of time. That is, for example, one or more standard bone screws 5may be used on one or both sides of the fracture F so that for someinitial period of time, for example, two or three weeks, micro-movementof the bone or bone fragments B is prevented so that the fracture sitecan be initially stabilized to facilitate initial callus formation. Thatis, days after initial fixation, tissue and/or cells may replicate andtransform so that the cells on either side of the fracture develop untilthey unite with their counterparts from the other side of the fracture.Eventually, the fracture F is bridged, restoring some of the bone'soriginal strength. Thereafter, removal of the standard bone screws 5from the surgical construct enables micro-movement of the bone/bonefragments B and/or enables distraction of the bone/bone fragments F. Inaddition, incorporation of one or more standard bone screws 5 may beused on one or both sides of the fracture F so that in cases ofnon-union, the bone or bone fragments B may be readjusted, repositioned,or alternative fixation may be applied.

Alternate Embodiments of the Dynamic Bone Fixation Element

Referring to FIG. 12, the dynamic bone fixation element 100 of a fourthpreferred embodiment may be in the form of an integrally formed dynamicbone fixation element. That is, the load carrier engaging component 140may be integrally formed with the bone engaging component 120 so thatthe shaft portion 150 may be integrally formed with the load carrierengaging component 140 and the bone engaging component 120. The dynamicbone fixation element 100 of the fourth preferred embodiment may achieveflexibility via the lumen 128 formed in the dynamic bone fixationelement 100. That is, due to the size and configuration of the shaftportion 150 and the lumen 128 formed in the bone engaging component 120,the head portion 142 is able to flex and/or move with respect to thebone engaging component 120.

In addition and/or alternatively, the dynamic bone fixation element 100of the fourth preferred embodiment may achieve flexibility via variousdesigns of a neck portion 131 (e.g., area between the bone engagingcomponent 120 and the load carrier engaging component 140). Preferably,material in the area of the neck 131 is removed in order to reducestructural stiffness. As a result of the removal of this material, thedynamic bone fixation element 100 becomes increasingly more flexible.For example, the dynamic bone fixation element 100 may be formed withone or more slots 190 in the neck portion 131. Slot(s) 190 may be formedin the neck portion 131 so that the neck 131 can function as a spring,allowing the neck portion 131 to flex, thereby allowing the head portion142 to move with respect to the bone engaging component 120. The shapeof the slot 190 formed in the neck portion 131 may be configured to takethe form of any one of a plurality of shapes and profiles. Differentprofiles may be provided to control axial and rotational movement. Forexample, a helical spring profile allows axial movement but generallydoes not block screw rotation, whereas a rectangular profile allowsaxial movement and generally blocks screw rotation. Alternatively, aV-shaped spring profile blocks screw rotation and generally limits axialmotion. The spring constant of the material and shape of the slots 190formed in the neck portion 131 of the dynamic bone fixation element 100may be used to control the movement of the head portion 142. Inaddition, additional element such as, for example, chamfers, conicalopenings, stiff pins, etc. may be incorporated as motion limitationmeans.

Referring to FIG. 13, the dynamic bone fixation element 100′ of a fifthpreferred embodiment may include a hollow volume 101′ formed in andthrough the neck portion 131′ such that a feather pin 150′ may belocated inside of the hollow volume 101′. In use, the feather pin 150′is similar to the shaft portion previously described however the featherpin 150′ may not be coupled to or engage both the bone engagingcomponent 120′ and the load carrier engaging component 140′. The featherpin 150′ may be, for example, integrally formed with the bone engagingcomponent 120′. The feather pin 150′ may extend from the bone engagingcomponent 120′ through the hollow volume 101′ of the neck portion 131′and into the head portion 142′ of the load carrier component 140′. A gap102′ is preferably provided between the outer surface 156′ of thefeather pin 150′ and the head portion 142′. As shown, the feather pin150′ preferably includes a head portion 151′ and a body portion 153′with the head portion 151′ having a larger diameter than the bodyportion 153′. The neck portion 131′ of the dynamic bone fixation element100′ preferably includes a plurality of slots 190′, as previouslydescribed in connection with dynamic bone fixation element 100. In use,the flexibility, both axial and compressive, is provided by the slots190′ formed in the neck portion 131′ of the dynamic bone fixationelement 100′. The flexibility may be limited by the size of the featherpin 150′ and the gap 102′ between the feather pin 150′ and the headportion 142′ of the dynamic bone fixation element 100′ such that whenthe dynamic bone fixation element 100′ is compressed, extended or movedaxially, the feather pin 150′ acts as a stop and limits the motiongenerally where, and when, the feather pin 150′ contacts the interiorwalls of the head portion 142′.

Referring to FIG. 14, the dynamic bone fixation element 100″ of a sixthpreferred embodiment may include a feather pin 150″ that is notintegrally formed with the dynamic bone fixation element 100″ but rathercoupled to a lumen 128″ formed in the bone engaging component 120″. Thefeather pin 150″ may be coupled to the lumen 128″ formed in the boneengaging component 120″ by any means as previously described.Furthermore, the neck portion 131″ of the dynamic bone fixation element100″ may be formed as a thin-walled hollow convex projection or bellowtype structure which preferably functions as a spring to provideelasticity and/or flexibility. The hollow convex projection or bellowtype structure may be further filled with a damper material topreferably control flexibility and protect the structural integrity ofthe dynamic bone fixation element 100″. The feather pin 150″ may beoptional and may be removed from the dynamic bone fixation element 100″.

Referring to FIG. 15, the dynamic bone fixation element 100′″ of aseventh preferred embodiment may include a damper material or an elasticelement 192′″ in the neck portion 131′″ (e.g., between the head portion142′″ and the bone engaging portion 120′″) of the dynamic bone fixationelement 100′″. A feather pin 150′″ preferably extends through the dampermaterial or elastic element 192′″. The damper material or elasticelement 192′″ may be fixed, axially moveable or rotatable with respectto the feather pin 150′″. In use, the damper material or elastic element192′″ acts as a damper.

With respect to the fifth, sixth and seventh embodiments of the dynamicbone fixation element (as shown in FIGS. 13-15), it should be noted thatthe feather pin 150′, 150″, 150′″ may be sized and configured to be anynumber of shapes and sizes. For example, the feather pin 150′, 150″,150′″ may include a head portion which may be cylindrical, conical,etc., and the body portion may be longer or shorter and may be tapered.Furthermore, the lumen formed in the dynamic bone fixation element maybe sized and configured to any number of different shapes and sizes, forexample it may be cylindrical, or it may be tapered, etc. Furthermore,it should be noted that while the ends of the feather pin 150′, 150″,150′″ are shown to be substantially circular, they may take on anygeometric profile such as, for example, polygon.

Referring to FIGS. 16A-16C, the dynamic bone fixation element 200 of aneight preferred embodiment may include one or more slots 247 formed inthe head portion 242 of the load carrier engaging component 240. Theslots 247 may extend into the head portion 242 from a distal end 246 ofthe head portion 242 (as shown in FIG. 16A). Alternatively, the slot 247may extend into the head portion 242 from a proximal end 244 of the headportion 242 (as shown in FIG. 16B). Alternatively, the slot 247 mayextend from a circumferential edge 249 of the head portion 242 towardsthe longitudinal axis 201 of the dynamic bone fixation element 200 (asshown in FIG. 16C). The slot 247 may be substantially parallel to thelongitudinal axis 201 of the dynamic bone fixation element 200 or may beangled with respect to the longitudinal axis 201 of the dynamic bonefixation element 200. Alternatively and/or in addition, the slot 247 maybe tapered, or alternatively the slot 247 may be straight or some otherconfiguration. In use, the head portion 242 may flex, with the size,taper, and location of the slot 247 defining the range of flexibility.It should be appreciated that the slots 247 may be modified to fit aparticular use of a dynamic bone fixation element 200, for example aslot 247 may have a larger or a smaller taper, it may extend less orfarther into the head portion 242, it may be angled to any degree, andmultiple slots 247 may be used.

Referring to FIG. 17, the dynamic bone fixation element 300 of a ninthpreferred embodiment may include a multi-piece head assembly therebypreferably forming one or more slots 347 in the head portion 342. Themulti-piece head assembly preferably includes a head portion 342, a bodyportion 350 and an optional damper material 394. The head portion 342preferably includes an aperture 343 through which the body portion 350is preferably inserted and to which it is preferably coupled. The headportion 342, aperture 343 and body portion 350 all being sized andconfigured so that one or more slots or gaps 347 are formed between thehead portion 342 and the body portion 350. The one or more slots or gaps347 are preferably filled with the damper material 394. It should beappreciated that depending on the use for which the dynamic bonefixation element 300 is intended, any type of slot or gap 347 may beincorporated into the head portion 342, and any amount of dampermaterial 394 may be used. In addition, or alternatively the slot or gap347 may be partially filled or completely filled with the dampermaterial 394. Further, it should be appreciated that coupling of thebody portion 350 to the head portion 342 may be performed by any methodincluding, but not limited to press fitting, a threaded connection,welding, pinning, shrinking, engrailing, etc. In addition, polymericcomponents or reduced structures such as flat springs, disk springs,meander shaped flat springs, etc. may also be incorporated.

The dynamic bone fixation elements 10, 10′, 10″, 100, 100′, 100″, 100′″,200, 300 (collectively 10-300) of the preferred embodiments may bemanufactured from any biocompatible material now or hereafter known inthe art including but not limited to titanium, a titanium alloy,stainless steel, etc. In addition, the dynamic bone fixation elements10-300 of the preferred embodiments may be coated to facilitateosseo-integration. For example, the bone engaging component 20, 20′,20″, 120, 120′, 120″, 120′″, 220, 320 (collectively 20-320) may becoated, for example, with a hydroxylapatite, or its outer surface may beroughened, perforated or subjected to surface treatments such as, forexample, anodic-plasma-chemical to embed hydroxylapatite into thetitanium-oxide surface layer. Alternatively and/or in addition, thedynamic bone fixation elements 10-300 of the preferred embodiments maybe coated to enable one or more semi- or non-biocompatible materials tobe used such as, for example, nickel, a nickel alloy, Ni—Ti-alloy (e.g.,Nitinol), stainless steel, a memory shaped alloy, cobalt chromium (CoCr)or a cobalt chromium alloy such as, for example, CoCrMo, CoCrMoC,CoCrNi, CoCrWNi, etc. For example, the bone engaging component 10-300may be manufactured from cobalt chromium molybdenum and the outerthreads may or may not be plasma coated with pure titanium.

The bone engaging 20-320 and load carrier engaging component 40, 40′,40″, 140, 140′, 140″, 140″, 240, 340 (collectively 40-340) may bemanufactured from the same material. Alternatively, the bone engagingcomponent 20-320 may be manufactured from a different material than theload carrier engaging component 40-340. For example, the bone engagingcomponent 20-320 may manufactured from a biocompatible metal, morepreferably one that is easily processible so that, for example, theexternal bone thread may be milled such as, for example, titanium, atitanium alloy, such as TAV (Ti-6Al-4V) or TAN (Ti-6Al-7Ni). The loadcarrier engaging component 40-340 may be made from a high strengthmaterial (e.g., R_(p) 0.2>1,000 MPA) in order to provide high elasticityand maximum stability. In addition, the load carrier engaging component40-340 is preferably manufactured from a material that providesresistance to fretting within the head-plate interface. The load carrierengaging component 40-340 may be made from, for example, a strong metalor metal alloy, such as CoCrMo, CoCrMoC, CoCrNi or CoCrWNi. In oneparticularly preferred embodiment, the bone engaging component 20-320 ismade from titanium or a titanium alloy such as, for example, TAV or TANwhile the load carrier engaging portion 40-340 is made from cobaltchromium (CoCr).

The damper materials used in some of the above exemplary embodiments maybe any material now or hereafter known in the art with dampingproperties including, but not limited to polymers, silicone, urethane,polycarbonate-urethane (PCU), elastic members of the polyaryletherketone(PAEK) family, elastic members of poly-esther-ether family, hydrogels,co-polymers, etc. The precise type and amount of damper material may bechosen based on the elasticity of the damping required.

It will also be understood by those of skill in the art that the use ofstrong metals and metal alloys in the dynamic bone fixation device10-300 prevents the galling of the dynamic bone fixation device 10-300to the load carrier 12. Drive damage is also prevented such thatcorrections of the load carrier 12 may be easily made.

The dynamic bone fixation elements 10-300 may be formed so that theydeform elastically when subjected to external forces as a result ofmicro-movement of the bone or bone fragments B to which they arecoupled. Thus, if later micro-movements of the bone or bone fragments Bare directed back toward an original position, the dynamic bone fixationelements will spring back to their original positions. Alternatively,the dynamic bone fixation elements 10-300 may be formed to plasticallydeform by the forces exerted during micro-movement of the bone or bonefragments B so that the dynamic bone fixation elements 10-300 retaintheir deformed shapes even after the forces imposed by themicro-movements have been removed. The dynamic bone fixation elements10-300 may be formed to deform with a substantially uniform springconstant (e.g., a force twice as great produces twice the deformation).Alternatively, the dynamic bone fixation elements 10-300 may be formedto remain substantially unflexed at all times until a force exerted bythe micro-movements exceeds a predetermined limit.

Generally speaking, in use movement of the load carrier engagingcomponent is preferably non-linear. More specifically, the shaft portionis preferably designed as a bendable pin so that the shaft portion iscapable of moving with respect to the bone engaging component and ableto give within a limited range. Referring to FIG. 3A, in an exemplaryembodiment of the dynamic bone fixation element and in order to optimizethe dynamic bone fixation element for maximum insertion torque versuselasticity of the shaft portion, the ratio of the outer diameter of thebone engaging component to displacement is between about 10 to about 20,and more preferably about 15. The ratio of the outer diameter of thebone engaging component to the outer diameter of the shaft portion isbetween about 1.4 to about 2.2, more preferably 1.8. The ratio of theouter diameter of the bone engaging component to the effective flexiblelength of the shaft portion is between about 3.5 to about 5.5, morepreferably 4.6. Exemplary sizes for the bone engaging component and loadcarrier engaging component are illustrated in Table 1.

TABLE 1 Exemplary Dimensions Outer Length Outer Diameter of of BoneTotal Diameter of Effective Bone Engaging Engaging Displace- the ShaftFlexible Component (d) Component (l) ment (c) Portion (d1) Length (lf)3.50 mm 26.00 mm +/−0.20 mm 2.00 mm 17.00 mm 5.00 mm 34.00 mm +/−0.30 mm3.00 mm 25.00 mm 6.20 mm 36.00 mm +/−0.50 mm 3.40 mm 23.00 mm 6.20 mm46.00 mm +/−0.50 mm 3.40 mm 30.00 mm

Dynamic Pedicle Screw Fixation Clamps

Pedicle screw fixation clamps are often used when bony structures, suchas facet joints or osteophites, would prevent a straightforward fixationof a rod into a pedicle screw. As a result, fixation clamps may be usedto bridge around such hurdles. In these cases it may be advantageous toprovide elasticity in the fixation clamps through, for example, theincorporation of a damper. For example, the damper may be in the form ofan elastic or polymeric component such as PCU, silicone, rubber, etc.Alternatively, the damper may be in the form of a spring such as flatsprings, disk springs, meander shaped flat springs, etc.

Referring to FIGS. 18A and 18B, the dynamic pedicle screw fixation clamp500 of a first preferred embodiment may include a bone screw 502 and aframe 510. The frame 510 preferably includes a pedicle screw clampingassembly 520 and a rod clamping assembly 530. The pedicle screw clampingassembly 520 preferably includes a clamping sleeve 522, a collet 524,and a locking mechanism 526 to secure and/or lock the position of thebone screw 502 with respect to the frame 510, although otherconfigurations for the pedicle screw clamping assembly 520 arecontemplated.

The rod clamping assembly 530 may be offset or located to the side ofthe pedicle screw clamping assembly 520. The rod clamping assembly 530preferably includes a recess 532, a clamp portion 534, a locking capportion 536 and a damper 550. The clamp portion 534 is preferably shapedlike a pedestal and includes a rod-receiving portion 542 attached to acolumn portion 540. The rod-receiving portion 542 preferably has aperimeter larger than the circumference of the column portion 540.Additionally, the rod-receiving portion 542 preferably has a length orperimeter that is slightly larger than the diameter of the recess 532formed in the frame 510. The column portion 540 is preferably sized andconfigured to be inserted into the recess 532 formed in the frame 510 sothat there is a clearance or gap between the outer surface of the columnportion 540 and the inner surface of the recess 532. Additionally, thecolumn portion 540 preferably has a height that is slightly larger thanthe height of the recess 532 formed in the frame 510 so that there is aclearance or gap between the bottom surface of the rod-receiving portion542 and the top surface of the frame 510. Preferably the gap between theouter surface of the column portion 540 and the inner surface of therecess 532 and the gap between the bottom surface of the rod-receivingportion 542 and the top surface of the frame 510 is filled with thedamper 550, more preferably a damper material.

The damper 550 is preferably annularly shaped and inserted into therecess 532 formed in the frame 510. The column portion 540 is preferablyinserted into the recess 532 and through a hollow cavity formed in thedamper 550 so that the column portion 540 is surrounded by the damper550. The frame 510 may also include an aperture 545 formed in the bottomsurface thereof in communication with the recess 532, the aperture 545being sized and configured to receive an end 542 of the column portion540. Preferably there is a clearance or gap between the end 542 of thecolumn portion 540 and the inner circumference of the aperture 545. Thedamper material 550 preferably is press-fitted or injection molded intothe recess 532 formed in the frame 510. Alternatively, the damper 550may be press-fitted or injection molded into another frame (not shown),which in turn would be press-fitted into the recess 532 formed in theframe 510.

In use, a rod 504 is preferably placed into the rod-receiving portion542 and clamped therein by the locking cap 536. In this position, therod 504 is free to move with respect to the frame 510 and with respectto the pedicle screw 502 due to the flexibility of the damper 550.Preferably, the clamp portion 534 is sized and configured to contact theframe 510 once the dynamic pedicle screw fixation clamp 500 has reacheda maximum angle of desired flex.

Alternatively, as shown in FIG. 18C, the clamping portion 534′ may havea rod receiving portion 542′ and an extension portion 560′, theextension portion 560′ may be a hollow cylindrical element that includesa plurality of slots forming flexible tabs 562′. In use, the flexibletabs 562′ are inserted into the recess 532′ formed in the frame 510′.The interior volume of the flexible tabs 562′ is preferably filled withthe damper 550′. In use, the slots provide additional flexibility to theclamping portion 534′ so that the bottom portion of the clamping portion534′ along with the damper 550′ permits movement of the rod 502′ due tothe flexibility of the damper 550′ and the resulting flexing of the tabs562′. In some embodiments, the rod-clamping portion 542′ may berotatable within the recess 532′ formed in the frame 510′.

Referring to FIG. 19, the dynamic pedicle screw fixation clamp 600 of asecond preferred embodiment may include a pedicle screw clampingassembly 620 and a rod clamping assembly 630 wherein the pedicle screwclamping assembly 620 and the rod clamping assembly 630 are in verticalalignment, as opposed to the side-by-side configuration of the firstpreferred embodiment. A damper 650, more preferably a damper material,is preferably located in between the pedicle screw clamping assembly 620and the rod clamping assembly 630 so that flexibility is providedbetween the pedicle screw clamping assembly 620 and the rod clampingassembly 630. Alternatively, the damper 650 may interconnect the pediclescrew clamping assembly 620 and the rod clamping assembly 630. Thedamper 650 may be fixed between the pedicle screw clamping assembly 620and the rod clamping assembly 630 by any mechanism including, forexample, via a frame, a ring, etc. Preferably, the damper 650 isinjection molded into and around the frame or ring 610 to connect thepedicle screw clamping assembly 620 and the rod clamping assembly 630together (as shown in the left side of FIG. 19).

Referring to FIGS. 20A and 20B, the dynamic pedicle screw fixation clamp700 of a third preferred embodiment may include a pedicle screw clampingassembly 720 and a rod clamping assembly 730. The rod clamping assembly730 may be offset or located to the side of the pedicle screw clampingassembly 720 via a frame 710. The frame 710, at the point wherein thepedicle screw clamping assembly 720 connects with rod clamping assembly730, preferably includes a plurality of slots 712 that provideflexibility between the rod clamp assembly 730 and the screw clampassembly 720. The slots 712 may take any shape or form as needed for theamount of flexibility that is desired.

Referring to FIGS. 21A and 21B, the dynamic pedicle screw fixation clamp800 of a fourth preferred embodiment may include a pedicle screwclamping assembly 820 and a rod clamping assembly 830. The rod clampingassembly 830 may be offset or located to the side of the pedicle screwclamping assembly 820 via a connecting member 810. The connecting member810 preferably includes a dynamic section 840. For example, the dynamicsection 840 may be in the form of a spring (as shown in FIGS. 21A and21B), a damper material, etc. In use, the dynamic section 840 ofconnecting member 810 allows flexing of the rod clamp assembly 830 withrespect to the screw clamp assembly 820. The dynamic section 840 may besized and configured to provide the level of flexibility that is desiredfor a particular application. The connecting member 810 may be coupledto the pedicle screw clamping assembly 820 and to the rod clampingassembly 830 by an mechanism know. For example, the connecting member810 may be coupled to the body of the screw clamp assembly 820 and maybe received within a connector clamp 832 located in the rod clampingassembly 830.

Referring to FIG. 22, the dynamic pedicle screw fixation clamp 900 of afifth preferred embodiment may include a rod/screw clamping assembly910, a locking ring 920 and a dynamic bone screw 902. The screw/rodclamping assembly 910 may be a side opening pedicle screw assembly. Thedynamic bone screw 902 and the rod 904 are preferably inserted intotheir respective receiving portions in the rod/screw clamping assembly910. In use, as will be appreciated by one of ordinary skill in the art,tightening of the rod 904 within the rod receiving portion causes therod 904 to press down onto the locking ring 920, which in turns causesthe screw receiving portion of rod/screw clamping assembly 910 totighten and clamp the dynamic bone screw 902. The dynamic bone screw 902however preferably incorporates one or more flexible elements so thatthe bone screw 902 can move or flex with respect to the rod 904. Forexample, the dynamic screw 902 may include a head portion 906 thatincludes a cavity for receiving a pair of beveled spring washers 907.The first beveled spring washer 907 a preferably is located on therod-facing end of the dynamic screw 902 with its center angled towardsthe second beveled spring washer 907 b, whereas the second beveledspring washer 907 b preferably is located adjacent to the shaft of thedynamic screw 902 with its center angled towards the first beveledspring washer 907 a. The dynamic screw 902 preferably also includes aridge 903 formed thereon, the ridge 903 being received between the twobeveled spring washers 907. The ridge 903 is preferably sized andconfigured to keep the beveled springs washers 907 from slipping.

In use, the beveled spring washers 907 flex, allowing the bonecontacting portion to deflect and flex relative to the head portion 906,and hence relative to the remainder of the pedicle screw assembly 900.Although two beveled spring washers 907 are shown and described, othertypes and amounts of springs are possible. Additionally, the bone screw902 may be received by the head portion 906 and/or attached to thesprings in any number of ways including, but not limited to, welding,gluing, etc. Depending on the type of springs, and method of attachmentof the springs that is used, the structure of the screw may be modified.For example, the screw may be configured not to have a ridge, or toinclude recesses or grooves to receive the springs, etc. Alternatively,as best shown in FIG. 23, the springs of the screw head design may bereplaced with a damper material 950, or alternatively the springs inFIG. 22 can be used with a damper material 950.

Referring to FIG. 24, the dynamic pedicle screw fixation clamp 1000 of asixth preferred embodiment may include a pedicle screw clamping assembly1020, a rod clamping assembly 1030 and a flexible element 1040 whereinthe flexible element 1040 is located between the rod clamping assembly1030 and the pedicle screw clamping assembly 1020. As shown, the rodclamping assembly 1030 may be in the form of a side opening rod clampingassembly. The pedicle screw clamping assembly 1020 is preferablysurrounded by a locking ring 1022. The flexible element 1040 connectingthe pedicle screw clamping assembly 1020 and the rod clamping assembly1030 is preferably made of a damper material. In use, the dampermaterial 1040 flexes, compresses and stretches to allow the pediclescrew clamping assembly 1020 to move with respect to the rod clampingassembly 1030. Although, a damper material element is described, the useof mechanical springs is also possible.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be understood that variousadditions, modifications, combinations and/or substitutions may be madetherein without departing from the spirit and scope of the invention asdefined in the accompanying claims. In particular, it will be clear tothose skilled in the art that the invention may be embodied in otherspecific forms, structures, arrangements, proportions, and with otherelements, materials, and components, without departing from the spiritor essential characteristics thereof. One skilled in the art willappreciate that the invention may be used with many modifications ofstructure, arrangement, proportions, materials, and components, whichare particularly adapted to specific environments and operativerequirements without departing from the principles of the invention. Inaddition, features described herein may be used singularly or incombination with other features. For example, features described inconnection with one embodiment may be used and/or interchanged withfeatures described in another embodiment. The presently disclosedembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims, and not limited to the foregoingdescription.

It will be appreciated by those skilled in the art that variousmodifications and alterations of the invention can be made withoutdeparting from the broad scope of the appended claims. Some of thesehave been discussed above and others will be apparent to those skilledin the art.

We claims:
 1. A dynamic bone fixation element configured to couple aload carrier to bone, the dynamic bone fixation element comprising: abone engaging component including a proximal end, a distal end spacedapart from the proximal end along a first direction, an inner surfacethat defines a lumen extending from the proximal end and toward thedistal end, and a plurality of threads that are configured to engagebone; and a load carrier engaging component including a head portionstructured to engage a load carrier and a shaft portion extending fromthe head portion along the first direction and into the lumen, the shaftportion having an outer surface that faces the inner surface such thatan air gap is defined between at least a portion of the outer surface ofthe shaft portion and at least a portion of the inner surface of thebone engaging component along a direction that is perpendicular to thefirst direction such that at least the head portion is moveable withrespect to the bone engaging component along a direction having adirectional component that is transverse to the first direction, whereinrotation of the load carrier engaging component about an axis thatextends substantially along the first direction causes the bone engagingcomponent to simultaneously rotate about the axis.
 2. The dynamic bonefixation element of claim 1, wherein a proximal portion of the lumen hasa diameter D_(L) and a proximal portion of the shaft portion has adiameter D_(S) that is less than the diameter D_(L).
 3. The dynamic bonefixation element of claim 2, wherein a distal end of the shaft portionhas a diameter greater than the diameter D_(L) of the lumen.
 4. Thedynamic bone fixation element of claim 2, wherein the inner surface istapered at an angle such that the diameter D_(L) of the lumen at aproximal end thereof is larger than the diameter D_(L) of the lumen at aposition distally of the proximal end.
 5. The dynamic bone fixationelement of claim 1, wherein a distal end of the shaft portion is coupledto the lumen at a position distal of the proximal end of the boneengaging component.
 6. The dynamic bone fixation element of claim 1,wherein the shaft portion is integrally formed with the head portion. 7.The dynamic bone fixation element of claim 1, wherein the shaft portionis welded to the bone engaging component within the lumen at a positionproximate to the distal end of the bone engaging component.
 8. Thedynamic bone fixation element of claim 7, wherein the outer surface ofthe shaft portion is welded to the inner surface of the lumen.
 9. Thedynamic bone fixation element of claim 8, wherein the outer surface ofthe shaft portion is welded to the inner surface of the lumen in-betweenadjacent threads of the bone engaging component.
 10. The dynamic bonefixation element of claim 1, wherein the shaft portion is coupled to thebone engaging component within the lumen with a press fit connection.11. The dynamic bone fixation element of claim 1, wherein the shaftportion includes one or more textured surfaces.
 12. The dynamic bonefixation element of claim 1, wherein the head portion includes a drivingelement configured to engage a tip formed on a drive tool.
 13. Thedynamic bone fixation element of claim 1, wherein the load carrierengaging component is made from cobalt chromium.
 14. The dynamic bonefixation element of claim 1, wherein the head includes external threads.15. The dynamic bone fixation element of claim 1, wherein the loadcarrier engaging component is welded to the bone engaging component sothat rotation of the load carrier engaging component about the axiscauses the bone engaging component to rotate about the axis.
 16. Thedynamic bone fixation element of claim 1, wherein rotation of the loadcarrier engaging component about the axis causes the outer surface toabut the inner surface so as to rotate the bone engaging component aboutthe axis.
 17. The dynamic bone fixation element of claim 16, wherein theinner and outer surfaces abut each other prior to the rotation.
 18. Thedynamic bone fixation element of claim 17, wherein the outer surface ispress-fit into the inner surface.
 19. The dynamic bone fixation elementof claim 1, wherein the shaft portion is movable relative to the boneengaging component.
 20. A dynamic bone fixation element configured tocouple a load carrier to bone, the dynamic bone fixation elementcomprising: a bone engaging component including a proximal end, a distalend spaced apart from the proximal end along a first direction, an innersurface that defines a lumen extending from the proximal end and towardthe distal end, and a plurality of threads that are configured to engagebone; and a load carrier engaging component including a head portionhaving external threads configured to mate with threads of a loadcarrier, and a shaft portion that extends from the head portion, througha hole of the load carrier along the first direction, and into the lumenwhen the external threads are mated with the threads of the loadcarrier, the shaft portion having an outer surface that faces the innersurface such that the outer surface of at least a proximal portion ofthe shaft portion is spaced away from the inner surface of at least aproximal portion of the bone engaging component along a direction thatis perpendicular to the first direction, such that at least the headportion is moveable with respect to the bone engaging component along adirection having a directional component that is transverse to the firstdirection.
 21. The dynamic bone fixation element of claim 20, wherein adistal portion of the shaft portion is coupled to a distal portion ofthe bone engaging component.
 22. The dynamic bone fixation element ofclaim 20, wherein the load carrier engaging component is a bone plateengaging component, the load carrier is a bone plate having a throughhole and internal threads surrounding the through hole, and the externalthreads of the head are configured to mate with the internal threads ofthe bone plate.
 23. The dynamic bone fixation element of claim 20,wherein rotation of the load carrier engaging component causes the boneengaging component to rotate.
 24. The dynamic bone fixation element ofclaim 20, wherein the proximal portion of the lumen has a diameter D_(L)and the proximal portion of the shaft portion has a diameter D_(S) thatis less than the diameter D_(L).
 25. The dynamic bone fixation elementof claim 21, wherein a distal end of the shaft portion has a diametergreater than the diameter D_(L) of the lumen.
 26. The dynamic bonefixation element of claim 20, wherein the distal portion of the shaftportion is welded to the distal portion of the bone engaging componentwithin the lumen.
 27. The dynamic bone fixation element of claim 26,wherein the outer surface of the shaft portion is welded to the innersurface of the lumen.
 28. The dynamic bone fixation element of claim 27,wherein the outer surface of the shaft portion is welded to the innersurface of the lumen in-between adjacent threads of the bone engagingcomponent.
 29. The dynamic bone fixation element of claim 21, whereinthe shaft portion is coupled to the bone engaging component within thelumen with a press fit connection.
 30. A method of making a dynamic bonefixation element, the method comprising: forming a bone engagingcomponent including a proximal end, a distal end spaced apart from theproximal end along a first direction, an inner surface that defines alumen extending from the proximal end and toward the distal end, and aplurality of threads that are configured to engage bone; forming a loadcarrier engaging component including a head portion structured to engagea load carrier and a shaft portion extending from the head portion alongthe first direction, the shaft portion having an outer surface that isconfigured to face the inner surface such that at least a portion of theouter surface of the shaft portion is spaced away from at least aportion of the inner surface of the bone engaging component along adirection that is perpendicular to the first direction; and welding thebone engaging component to the load carrier engaging component betweenadjacent threads of the bone engaging component.
 31. The method of claim30, further comprising the step of press-fitting the shaft portion intothe lumen.
 32. A method of affixing a bone plate to first and secondbone fragments, the method comprising: inserting a dynamic bone fixationelement into an opening of a bone plate, the dynamic bone fixationelement having a bone engaging component, and a bone plate engagingcomponent, the bone engaging component includes an inner surface thatdefines a lumen extending along a first direction, and the load carrierengaging component includes a head portion having external threads, anda shaft portion that extends from the head portion along the firstdirection and into the lumen, the shaft portion being coupled to thesleeve within the lumen such that the head is moveable with respect tothe bone engaging component along a direction having a directionalcomponent that is transverse to the first direction; rotating thedynamic bone fixation element so as to advance the dynamic bone fixationelement through the opening such that the external threads of the headengage internal threads of the opening in the bone plate, and externalthreads of the bone engaging component engage a bone fragment.
 33. Themethod of claim 32, wherein the step of rotating the dynamic bonefixation element comprises rotating a drive tool that is mated with adriving element defined in the head of the bone plate engagingcomponent.
 34. The method of claim 33, wherein the bone plate engagingcomponent and the bone engaging component are simultaneously rotated.35. A dynamic bone fixation element configured to couple a load carrierto bone, the dynamic bone fixation element comprising: a bone engagingcomponent including a proximal end, a distal end spaced apart from theproximal end along a first direction, an inner surface that defines alumen extending from the proximal end and toward the distal end, and aplurality of threads that are configured to engage bone; and a loadcarrier engaging component including a head portion structured to engagea load carrier and a shaft portion extending from the head portion alongthe first direction and into the lumen, the shaft portion having anouter surface that faces the inner surface such that at least a portionof the outer surface of the shaft portion is spaced away from at least aportion of the inner surface of the bone engaging component along adirection that is perpendicular to the first direction such that atleast the head portion is moveable with respect to the bone engagingcomponent along a direction having a directional component that istransverse to the first direction, wherein rotation of the load carrierengaging component about an axis that extends substantially along thefirst direction causes an abutment between the outer surface and theinner surface to drive rotation of the bone engaging component about theaxis simultaneously with the rotation of the load carrier engagingcomponent.
 36. The dynamic bone fixation element of claim 35, whereinthe inner and outer surfaces abut each other prior to the rotation. 37.The dynamic bone fixation element of claim 36, wherein the outer surfaceis press-fit into the inner surface.
 38. The dynamic bone fixationelement of claim 35, wherein the shaft portion is welded to the boneengaging component.
 39. The dynamic bone fixation element of claim 38,wherein the shaft portion is welded to the bone engaging componentbetween adjacent threads.